In a thin film fabricating process, atomic layer deposition (ALD) or cyclic chemical vapor deposition (cyclic CVD) has been studied to further improve physical properties of a thin film.
The principle of the ALD is as follows. If a first source gas is fed into a reactor in a gaseous state, the first source gas reacts with a substrate surface, and thus a monatomic layer is chemically absorbed. If the surface is saturated with the first source gas, the first source gas over the atomic layer is physically absorbed due to non-reactivity between the same ligands. The first source gas which is physically absorbed is removed by a purge gas. When a second source gas is fed onto the first layer, a second layer is grown through substitution reaction between ligands of the first and second source uses. Since the second source gas which does not react with the first layer is physically adsorbed, the second source gas is removed by the purge gas. A surface of the second layer is in a state of reacting with the first source gas. The above-described processes constitute one cycle, and a thin film is deposited by repetition of the cycle.
In order to stably maintain the ALD reaction in the reactor, the first source gas and the second source gas should be fed into the reactor while being separately not to be mixed with each other the gaseous state. According to a conventionally general method, the first source gas and the second source gas are fed into the reactor via different gas feed lines at time intervals. A process of separately feeding the purge gas is employed between the feed of the first source gas and the second source gas to remove the residual gas in the reactor. Valves are used to feed the first source gas, the second source gas, and the purge gas at time intervals.
In order to increase a deposition speed and prevent waste of the source gases in the ADL, it is preferable to feed the source gas only by a surface saturation time of the source gases. However, since the surface saturation time is usually less than one second, the valves should be operated several times within a short period. If the valves are operated many times within the short period, there is a problem of rapidly shortening a lifetime of the valves. The whole processing time is affected by a fact that extra source gases are quickly exhausted, and there is a problem in that the whole processing time may be extended if the gas of poor exhaust is used.
Since a complicated gas feed line for feeding the source gases into the reactor and thus a plurality of valves are provided to adjust the source gases when a kind of the source gases is increased, a problem of increasing a cost and assuring an installation space happens. Further, capacity of hardware and software for adjusting the feed of the source gas should be increased. In addition, since each amount of the source gases and the purge gas fed into the reactor is different, pressure in the reactor is frequently varied, so that stability of the process becomes a problem.
As a result, the complexity of the valves and the frequent operation of the valves increase a maintenance cost of the equipment, as well as shortening the lifetime of the valves. Further, since a shutdown time of the equipment caused by the maintenance is increased, its productivity is lowered.
A metallic thin film used in a conventional semiconductor element has a low resistance value, and if it is deposited on a rear surface of the substrate, it causes a lifting problem and degrades an electric property of the semiconductor element. Accordingly, the most of metallic thin film deposition apparatuses are realized by a single wafer-type chamber, rather than a furnace-type chamber for implementing the deposition on only a front surface of the substrate. However, if the metallic thin film is deposited through ALD or cyclic CVD in the single wafer-type chamber, there is a problem in that its productivity is lowered since a deposition time is extended.